Propeller blade



March 6, 1934. F. J. MARTENS ET AL 1,949,611

PROPELLER BLADE Filed Sept. 14, 1932 E'd. Mar-fans Patented Man .6,' 1 934 PROPELLER BLADE Fred J. Martens and Clinton 0. Thompson, Mllwaukee, Wis., assignors of one-third to Edward A. Wilke and Mae V. Wilke, Milwaukee, Wis.

Application September 14, 1932, Serial No. 633,029

2 Claims.

This invention appertains to propellers susceptible for advantageous use wherever propellers or fans are applicable,'but which is particularly adapted for aeronautical purposes.

In our allowed application, Serial No. 569,533, filed July 21, 1930, a propeller was shown in which each blade thereof embodied a pair of airfoils arranged in a predetermined manner. This structure has its advantages as fully set forth in said application and the present invention relates more fully to the formation of an airfoil for a propeller, whether the blades are of a single or double airfoil type.

Many attempts have been made to provide a propeller in which the pitch angle of the blades can be varied or changed during flight, so as to obtain the best advantages during take-off, landing and free flight and according to load, ceiling, etc. However, in all of the constructions with which we are familiar, an ordinary propeller blade is used and the improvements consist in the means for turning the blades in the hub. While the changing of the pitch angle of the blades for different purposes was theoretically correct, in practice the desired results could notbe obtained due to the shape of the blades themselves, as when the pitch angle was varied, the desired pitch might be obtained at the hub end of the blades but the tip ends might actually be in reverse from 3 what was desired.

It is therefore a salient object of our invention to provide an improved propeller blade or airfoil which is so constructed that the maximum amount of efliciency will be obtained therefrom irrespective of the pitch angle at which the blade is set.

A further salient object of our invention is to provide a propeller blade or airfoil in which the major portion of the blade is offset from the 0 center line of the root of the blade and whereby during changing of the pitch angle of the blade, an actual raising and lowering movement of the blade tip is effected, .so that the desired pitch angle will be obtained throughout the,entire length of the blade, thereby renderingthe entire blade active during rotation and permitting ,the blade to follow a natural geometrical helix during rotation;

Further objects and advantages of our invention will more fully appear as the description proceeds'and references had to the accompanying drawing, in which:

Figure 1 is a front elevation of a propeller hub with our improved blade attached thereto, the blade being set at an "a" pitch.

Figure 2 is a side elevation of a propeller hub showing our blade connected therewith and set at an 8 pitch.

Figure 3 is an end view looking from'the tip of theblade toward the hub showing the blade set at an 8 pitch in full lines and at a 10 pitch in dotted lines.

Figure 4 is a cross section through the blade or airfoil taken at station I adjacent to the stem of the blade.

Figure 5 is a cross section through the blade taken at station E.

Figure 6 is a cross section through the blade taken at station E and adjacent to the tip of the blade.

Referring more particularly to the drawing, the numeral 10 generally indicates our improved propeller blade or airfoil which embodies a root 11 mounted within the hub 12 either for turning movement or against turning movement. This hub 12 is fixed in any desired manner to the propeller shaft 13. The blade roots are arranged substantially tangential to the propellershaft; but can be radially disposed relative to the shaft if desired. The body portion '14 of the blade 10 is connected by means of a stem 15 with the root 11 and this stem can be formed substantially thick for structural strength, as shown in Figure 4 of the drawing.

.By referring to Figure 1 of the drawing, it will be noted that the body portion 14 of the blade departs from the stem 11 and extends across the center line K of the axis of the propeller shaft and the tip '16 of the blade extends on the other side of this center line K from the stem. The blade gradually tapers from the leading edge 17 toward the trailing edge 18. By referring to Figures 1, 2 and 3, it will be noted that the tip 16 of the blade is eccentrically disposed relative to the center line L of the axis of the blade root 11.

The blade back face is used in checking the pitch angles at the different stations along the blade face and no divergence is made from the results obtained in relation to the center line M through the blade length. This center line M is 1 at an acute angle to the center line L of the axis of the blade root.

The blade is originally laid out at a pre-ascertained pitch on the natural geometrical helix starting at the root. The various stations are progressively indicated by the letters 4lI, inclusive, and these stations are taken at different points from the tip to the stem. Attention is in vited to the off-center line, rear to direction of rotation and following through tip with off-center.

line ahead of direction of rotation and placed at vantage points ahead of center line of axis of propeller shaft in direction of helix lead.

The complication of angles will cause an eccentric which pivots around approximately at station E and permits blade length leading edge at tip and trailing edge at or near root to travel and required distance to obtain a true helix with a change of approximately five given pitch changes. Thus, the blade positively maintains a uniform pitch angle through the blade length.

In changing from one pitch to another, say from and 8 pitch to a 10" pitch as shown in Figure 3 of the drawing, the following pitch angles will result:

The station A at an 8 pitch, a pitch angle of 14 1'7 min. is had, while the station I a pitch angle of 51 37 min. is had. When the blade is changed to 10 pitch, the blade tip at station A will move forward as a whole but slightly rearward at leading edge to result in a change of about 3 20 min., while at station I will allow a change of approximately 6 30 min. This results in 10 pitch with station A 17 39 min. and station I 57 51 min.

Stations A J, inclusive, are drawn tangent to radius lines through which angle readings are taken.

I From the foregoing description, it can be seen that we have provided an efficient propeller blade or airfoil in which we are enabled to obtain the desired true pitch angle throughout" the entire length when the blade is turned.

Changes in details may be made without departing from the spirit or the scope of this invention, but what we claim as new is:

1. A propeller blade embodying a body, a stem and a tip, with the stem lying on one side of center line of axis of the propeller shaft and the tip lying on the other side of the center line of axis of the propeller shaft.

2. A propeller blade comprising a stem, a body and a tip, with the stem lying. on one side of the center line of the axis of .the propeller shaft. and the tip lying onthe other side of the center line of the axis of the propeller shaft, the body being gradually tapered from its tip and gradually decreasing in" width from its leading edge to its trailing edge, the tapered tipbeing eccentrioaglly disposed relative to the center line ofaxis of the v 

